The present invention relates generally to laser beam scanning, and, more specifically, to barcode scanners.
In a typical laser barcode scanner, a laser beam is projected at a rotating spinner having several mirror facets from which the laser beam is reflected at different angles. The reflected beams meet corresponding pattern mirrors which steer the beams out a common window above which a barcode is positioned. The barcode may take any conventional form such as the Universal Product Code (UPC) which includes a series of dark bars and light spaces therebetween of varying widths for encoding desired data.
The barcode is read by traversing the laser beam as a scan line across the successive bars and spaces for producing reflected light which varies in intensity corresponding therewith. The so modulated reflected light is reflected back into the scanner wherein it is detected by a photodetector and decoded in a conventional manner to correspondingly decode the barcode itself.
Since the barcode may be positioned atop the scanner window in various orientations, the spinner facets and cooperating pattern mirrors are selected for producing an intersecting pattern of scan lines across the barcode for ensuring that at least one scan line properly traverses the barcode. Accordingly, the pattern mirrors must be differently oriented in space and spaced apart from each other. The spinner facets are oriented at different inclination angles atop the spinner. Each spinner facet therefore traverses a group of pattern mirrors as the spinner rotates for producing a corresponding set of short scan lines which are projected through the scanner window. The scan line set for each spinner facet is different to produce the entire scan pattern.
However, this configuration is boxy and has a correspondingly large space requirement. The facets mounted on the spinner limit the rotational speed of the spinner in view of the large size thereof.
Another type of barcode scanner was unsuccessfully placed in commercial use in the last decade based on the principle of holography. In the holographic barcode scanner, a specially configured holographic deflector was rotated for diffracting laser light for producing scan lines. This scanner was not commercially viable apparently for the difficulty and attendant cost of manufacturing the holographic deflector.
The holographic deflector includes a hologram manufactured by exposing a suitable medium, such as silver halide, using two incident laser beams in a specific orientation to create a hologram having an interference fringe pattern. The resultant hologram must be accurately positioned in the scanner for receiving the incident laser beam along the same path as used in forming the hologram originally. Light diffracted from the hologram is then used as a scan line projected outwardly in a predetermined path based on the original orientation of the beams producing the hologram.
Accordingly, it is desired to produce a simpler and more compact barcode scanner without the need for complex and costly holograms.